Get a tire plug kit. Then practice on your stock spare tire to learn how to use it.
Takes up very little space, and I've never had a "flat" I could not plug in a few moments. (Generally some nail or bolt, or even a bungie cord hook that my tire picked up through the tread.)
I have taken some in and had them patched after they have been plugged, and no problems. But I've also run into shops that will not work on them after you use fix a flat type can sealers as IJ noted. (But I still carry both the plugs, and the fix a flat.. I really should get a small compressor....)
A few years ago, when I worked Hurricane Ivan, my rental Tar-ass had picked up so many nails, and other metal debris, that I had 6 large cans of fix-a-flat in the wheels, and multiple plugs. (Expensed the lot.. LOL) Other people I was working with had flat tires, or were stranded and cussing about having to change out the spare, and then the spare had a flat... LOL I just showed them the cans of fix a flat, and the plug kit, plus a few plugs sticking out of the tires..
There was a run on WalMart for the cans and the plugs! No more flats, no more problems, and Hertz can deal with it. (My rental car was so un-ballanced by the end of two weeks, that It was like a washing machine on the spin cycle at 80mph.. I don't know what was more annoying, the vibes, or the damn Neverlost woman's voice telling me where to drive...
)